1. Field of the Invention
The invention relates to a more industrially and commercially advantageous form of carbon black and to processes for its production and use. Carbon black is a generic term for a class of particulate or powdery products composed essentially of elemental carbon. Carbon black is used principally as a filler or reinforcing agent in rubber, as a pigment, or for its electrically conductive properties. Carbon blacks may be categorized by their modes of production and by their physical characteristics, such as particle shape or size and their degree of aggregation or agglomeration. The carbon blacks of the present invention have a number of advantageous properties, including superior dispersibility, compared to conventional carbon blacks.
2. Description of Related Art
The carbon-black production processes that are most important industrially are based on the oxidative pyrolysis of carbonaceous carbon-black raw materials. In these processes the carbon-black raw materials are subjected to incomplete combustion at high temperatures in the presence of oxygen. This class of processes for producing carbon black includes, for example, the furnace-black process, the gas-black process and the flame-black process. Polynuclear aromatic carbon-black oils are predominantly employed as carbonaceous raw materials for the production of carbon-black.
Oxidative pyrolysis produces a stream of products including waste gases containing hydrogen and carbon monoxide and finely divided carbon black suspended in the waste gases. The carbon black is separated from the waste gas in a filtration plant. The carbon black thus prepared may be prepared for further processing by pelletization. Pelletization is usually performed using a wet or dry granulating process and produces pelletized black. Additionally, a conclusive drying operation may be used to reduce the moisture content of the carbon black to below 1 wt. %.
Over 90% of the carbon blacks produced industrially are employed as fillers and as reinforcing agents in the production of rubber mixtures. For instance, one important application for such rubber mixtures is in the production of highly-filled profiled joints in automobile manufacture. Typical rubber mixtures of such a type contain 20 to 40 wt. % synthetic rubber, preferably EPDM, 20 to 50 wt. % carbon black, mineral oil and further auxiliary substances. Such rubber mixtures may also contain sulfur or peroxides as vulcanizing agents.
The properties of manufactured products, such as profiled joints, are influenced by the specific properties of the carbon black component. For instance, the choice of a carbon black influences the viscosity of, the injection speed, the swelling after extrusion, the filler dispersion, the hardness, the compression set and many other properties of a rubber or synthetic rubber mixture used in the manufacture a profiled joint. Economical and convenient production of such products demand a form of carbon black that provides low swelling after extrusion, a high injection speed and a good dispersibility at given hardness.
An important variable influencing the functional properties of such mixtures is the specific surface area of a carbon black, in particular, the CTAB surface area, which is a measure of the rubber-effective surface portion of the carbon black. Injection speed and dispersibility rise with diminishing CTAB surface area.
Other important carbon-black parameters are the DBP absorption as a measure index for the initial structure and the 24M4-DBP absorption as a measure of the residual structure still remaining after mechanical stressing of the carbon black. High DBP values result in good dispersibility and low swelling after extrusion. Characterization of carbon black using CTAB surface area or DBP absorption, as well as other conventional parameters or test methods, is described by The Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition (1992), vol. 4, pages 1037-1074.
Carbon blacks that exhibit CTAB surface areas between 10 and 50 m2/g and DBP absorption values between 80 and 160 ml/100 g are suitable for profile mixtures.
Furnace blacks with a low iodine number and high DBP values are known from EP 0609433.
Among the disadvantages of the known carbon blacks is their poor dispersibility and poor processability during manufacturing processes. While such carbon blacks may have low specific surface areas and high structure, the increasingly critical formulations based on partially crystalline EPDM types and, conditioned by economic considerations, the increasingly shorter mixing-times, highlight the need for a more dispersible and conveniently processed form of carbon black.
Accordingly, one object of the present invention is to provide a carbon black that is more easily and economically dispersed and processed for industrial and commercial applications, especially in the production of rubber-profile mixtures. Other objects of the invention include provision of a form of carbon black that reduces swelling of a rubber mixture after extrusion, a form of carbon black that permits more rapid extrusion of a rubber mixture, and/or a form of carbon black that permits high filler loadings in a rubber mixture. Other objects of the invention include processes for making the above-mentioned forms of carbon black and products or compositions comprising such carbon blacks. Additionally, still other objects of the invention will be evident from the following description.